First-principles study of LiFePO4 modified by graphene and defective graphene oxide

The energy stability and electronic structural of graphene and defective graphene oxide (GO) parallel to the surface of LiFePO4 (010) were theoretically investigated by using first-principles density functional theory calculations within the DFT + U framework. The calculated formation energy shows that GO coating on the surface of LiFePO4 (010) is energetically favorable and has higher bond strength compared to graphene. The calculation of the electronic structure indicates that the emergence of band in-gap states originates from graphene coating, with adsorbed O atoms contributing significantly above the Fermi level. Electron density difference indicate that GO stands on the LFP (010) surface through C-O and Fe-O bonds, rather than relying on van der Waals forces placed parallel to the LFP crystal, with the chemical bond at the LFP/GO interface (Fe-O-C) both anchoring the coated carbon layer and promoting electron conductivity at the interface. In addition, LFP/GO shows superior electrochemical performance, Atomic Populations suggests that the average Fe-O bonding on the surface of LiFePO4 (010) was clearly changed after graphene or GO coating, which led to the expansion of Li+ channels and favored the migration insertion and extraction of Li+.

The structural, stability, electronic, optical and thermodynamic properties of MoX2 (X= S, Se, and Te) under hydrostatic pressures: a plasmon approach and first-principle study

CONTEXT

The new equations have been developed for the structural and electronic properties using the plasmon calculations for the first time for 2-D MoX2 structures. Literature shows still an extensive study is required on the stability and optical properties of MoX2 under different hydrostatic pressures and thermal properties under different temperatures using the first principles, for electronic industrial applications. The stability is analyzed using binding energy and phonon calculations. The phase transition of metallization of MoX2 is discussed using band structure calculations under different hydrostatic pressures. The calculated work function shows the photoemission starts from the threshold frequency of 4.189×104 cm-1, 3.184×104 cm-1, and 3.651×104 cm-1, respectively, for MoS2, MoSe2, and MoTe2 materials. The optical properties such as refractive index n(0), and static dielectric permittivity ε(0) for three successive materials are calculated under different hydrostatic pressures, applicable for optoelectronic applications. The calculated theoretical and computational values agree well with each other and also agree with reported and experimental values. Some of the values are calculated for the first time.

METHODS

The theoretical equations are derived using the molecular weight, effective valence electrons, and density of molecule of MoX2 structures. The simulation work is performed using GGA-PBE approximation in the CASTEP simulation package with DFT+D semi-empirical dispersion correction. An ultra-soft pseudopotential representation calculates the electronic and optical properties with a finite basis set kinetic energy cut-off of 381.0 eV. Each geometry has been optimized using Broyden, Fletcher, Goldfarb, and Shanno's (BFGS) algorithm for 100 iterations with a fixed basis quality variable cell method and finite electronic minimization parameters. The phonon calculations were performed using TDFT with a kinetic energy cut of 460 eV in a norm-conserving linear response method. The interpolation with a finite dispersion quality and q-vector grid spacing is performed.

Bending deformation modulation of the optoelectronic properties of molybdenum ditelluride doped with nonmetallic atoms X (X = B, C, N, O): a first-principles study

CONTEXT

A first-principles approach based on density functional theory was used to explore the effect of bending deformation on the electrical structure of molybdenum ditelluride doped with nonmetallic atoms X (X = B, C, N, and O). The study included alternate doping of nonmetallic atoms, as well as a comparison of the effects of intrinsic bending deformation and nonmetallic doping deformation. The results demonstrate that boron atom doping raises the Fermi energy level. Examining the energy band structure indicates that the intrinsic molybdenum ditelluride is a direct band gap semiconductor, which is transformed from a direct band gap to an indirect band gap after doping. We selected boron-doped systems for bending deformation and compared them with the intrinsic systems. With increasing deformation, all systems start to shift from semiconductor to metal. When the deformation reaches 8°, the energy levels fill and the electron energy increases. The intrinsically bent systems transition from direct band gap to indirect band gap and eventually to metal. The indirect band gap semiconductor-to-metal transition process occurs after the bending deformation of the boron-doped atoms. The analytical results show that the absorption and reflection peaks of the molybdenum ditelluride system are blue-shifted after the bending deformation of the boron-doped atoms.

METHODS

Under fundamental principles, this research depends on the density functional theory framework (DFT) using the CASTEP module in the Materials-Studio software. The plane-wave pseudopotential approach with modified gradient approximation and the Perdew-Burke-Ernzerhof (PBE) generalized function is used for structure optimization and total energy calculations of the X-doped (X = B, C, N, O) MoTe2 system at different shape variables. Geometry optimization of the 27-atom superlattice MoTe2 was carried out, followed by alternative doping of tellurium atoms in the molybdenum ditelluride with B, C, N, and O. In this paper, the intrinsic bending deformation and B-doping of molybdenum ditelluride were selected for deformation analysis. Intrinsic bending deformations and boron-doped molybdenum ditelluride with bending angles ranging from 2° to 8° were employed for deformation investigation. In Fig. 1, pink is used to represent doped B atoms, orange is used to describe Te atoms, and green is used to represent Mo atoms. For the degree of deformation of molybdenum ditelluride, in this paper, it is expressed by the bending angle, i.e., the angle of the plane of molybdenum ditelluride after bending and deformation of a single layer of molybdenum ditelluride concerning the angle of the plane folded for the deformed plane. How to do it: For ease of presentation, the atomic chains are set to different colors. The purple part on both sides of the figure is bent and deformed, 3-5 atoms are fixed appropriately, and the middle part is deformed. On this basis, the bending deformation of intrinsically doped and boron-doped MoTe2 is comparatively analyzed. The effect of boron-doped atoms on the structure of MoTe2 is systematically investigated to study its structural stability and electronic structure. Fig. 1 a1 and a2 The main and side views of intrinsic MoTe2; b1 and (b2) the main and side views of MoTe2 doped with boron atoms bent by 8°.

Electronic structure and optical properties of In- and Vacancy-doped 6H-SiC: a first-principles study

PURPOSES

The paper aims to investigative the cacuses and impacts of In- and Vacancy-doped to 6H-SiC, expecting that improving optical properties of materials. Design-Using the first-principles calculations, we discuss the electronic structure and optical properties of different doped 6H-SiC systems.

FINDINGS

The results show that In-doped 6H-SiC becomes a direct bandgap p-type semiconductor and the energy bandgap is reduced from the intrinsic 2.059 to 1.515 eV. We demonstrate the stability of the systems through the formation energy analysis, meanwhile identify their physical origins and discuss applications of all structures in electronic devices within optical analysis. Find the energy beginning values of the VSi-doped and VC-doped systems' optical absorption spectrums and extend to 0.4 2 eV and 0.11 eV respectively compared with the original 3.23 eV. In the visible light region, the reflectivity images of the VC/VSi and (In, VSi)-codoped systems rise obviously.

CONCLUSIONS

The optical properties of all doping systems were analyzed to be improved compared with the intrinsic, all above mentioned provide a theoretical basis for the fabrication of spintronic and optical devices.

Curvature effects regulate the catalytic activity of Co@N4-doped carbon nanotubes as bifunctional ORR/OER catalysts

The advancement of metal-air batteries relies significantly on the development of highly efficient bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we investigate the potential application of Co@N4-doped carbon nanotubes (Co@N4CNTs) as bifunctional catalysts using density functional theory calculations. We explore the stability and electronic properties of Co@N4CNTs by analyzing energies, bond lengths, conducting ab initio molecular dynamics simulations, and examining the density of states. Notably, the diameter of the nanotubes has a notable impact on the catalytic performance of Co@N4CNTs. A remarkable 54% improvement in catalytic activity when transitioning from (4, 4) to (24, 4) Co@N4CNTs, with ηBi from changing from 1.40 to 0.64 V. We have several exceptional catalysts with low overpotentials, including (18, 4), (22, 4), and (24, 4) Co@N4CNTs, which exhibit ηBi values of 0.68, 0.67, and 0.64 V, respectively. Moreover, we link the increased activity of Co@N4CNTs to the change of Co atom's partial d orbital energy, facilitated by adjustments in the diameter of Co@N4CNTs. This revelation offers valuable insights into the underlying factors driving the enhancement of catalytic activity through alterations in orbital energy levels. Our research uncovers several excellent catalysts and provides valuable insights for the design and development of efficient catalysts for metal-air batteries.

Effect of Mn, N co-doped LiFePO4 on electrochemical and mechanical properties: A DFT study

In this study, the thermodynamic stability, embedding voltage, volume change rate, electronic structure properties, mechanical properties and lithium-ion diffusion characteristics of the Mn, N co-doped LiFePO4 material are investigated using a first-principles approach based on density generalization theory. The results show that the doped system has a low formation energy and the material meets the thermodynamic stability criteria. During the de-lithium process, the volume change rate of the doped material decreases and the cycling performance is improved, but the battery energy density decreases slightly. It is also found that the doping of N led to the transformation of the material from a p-type semiconductor to an N-type semiconductor, while the doping of Mn and N lead to the creation of impurity bands, narrowing of the band gap and an increase in conductivity. At the same time, Mn, N co-doping greatly improve the ductility of the material, suppress the generation of microcracks, and reduce the possibility of shear deformation. In addition, it is noteworthy that the lithium-ion diffusion energy barrier of the doped system is reduced, which predicts an increase in the diffusion rate of lithium ions in the doped system.

First-principle study on the geometric and electronic structure of Mg-doped LiNiO2 for Li-ion batteries

CONTEXT

Ni-rich layered oxides have been widely studied as cathodes because of their high energy density. However, the gradual structural transformation during the cycle will lead to the capacity degradation and potential decay of the cathode materials. In this paper, first-principle calculations were used to investigate the formation energy, and geometric and electronic structure of Mg-doped LiNiO2 cathode for Li-ion batteries. The results show that Mg doping has little effect on the geometric structure of LiNiO2 but has great effect on its electronic structure. Our data give an insight into the microscopic mechanism of Mg-doped LiNiO2 and provide a theoretical reference for experimental research, which is helpful to the design of safer and higher energy density Ni-rich cathodes.

METHOD

In this work, all calculations were performed by the VASP package; the PBE functional in the generalized gradient approximation (GGA) was employed to describe the exchange-correlation interactions. An energy cutoff of 520 eV and a 5 × 5 × 3 Monkhorst-Pack mesh of k-point sampling in the Brillouin zone were chosen for all calculations. All atoms were relaxed until the convergences of 10-5 eV/f.u in energy and 0.01 eV/Å in force were reached.

Electronic and optical structural manipulation of NbS2 defects under strain: first-principles calculations

CONTEXT

Monolayer NbS2 is a promising new two-dimensional material, and it is critical to develop effective methods to make NbS2 a material for nanodevices and photovoltaic applications. This study studied the strain rule of sulfur-deficient NbS2 structure by first principles. The results show that all defect structures introduce impurity states to enhance electron transport. The disulfide defect structure produces an indirect band gap under the action of tensile strain, which can reach up to 0.56eV and become a diluted semiconductor. The hybrid NbS2 exhibits high transparency under infrared, visible, and low-frequency ultraviolet light, improving the material's transmittance, optical response, and catalytic activity. The research results of this paper will provide a basis for the subsequent research of single-layer NbS2 and accelerate the research process of NbS2 as a new semiconductor material.

METHODS

We are on the surface perpendicular to the 3×3×1 NbS2 and use a 15 Å vacuum layer to avoid interacting with periodic images. The first-principles simulation uses the CASTEP module in Materials Studio to simulate the hypothetical model and relaxation optimization structure of single-layer NbS2 under strain and defect state. The calculation function is PBE (Perdew-Burke-Ernzerhof) function under the generalized gradient approximation (GGA) for an approximate calculation to describe the interaction between electrons and the interaction between electrons and ions. The pseudopotentials of 3s23p4 and 4d45s1 valence electron configurations were used for S and Nb atoms, respectively. Van der Waals correction is considered in the simulation process. Moreover, it includes spin-orbit coupling (SOC) effects. For the plane wave truncation energy, we set it at 500eV. The arrangement of the Brillouin area is divided by 6×6×1 gamma-centered Monkhorst-Pack grids. The lattice deformation of all hybrid structures is less than 0.05 Gpa, and the interatomic force is less than 0.03 eV/Å.

Theoretical investigation of adsorption characteristics of typical additives for zinc electroplating

CONTEXT

Electroplated zinc layers have shown excellent corrosion resistance, especially those are stable in the atmosphere after the passivation, and therefore zinc electroplating is widely used in various fields such has mechanical, vehicle, construction, and ironware industries. Benzalacetone (BA) was reported as brighteners for zinc deposition, while polyoxyethylene nonylphenylether (NP) was used as levelers or carriers for zinc electroplating. Sodium benzoate (SB) and dispersant NNO cooperatively act as auxiliary additives. Quantum chemical parameters (QCPs) of four additives were calculated by using DFT, and MD simulations were performed. By comparing binding energies of four additives (benzalacetone (BA), sodium benzoate (SB), polyoxyethylene nonylphenylether (NP) and dispersant NNO), with Zn (001) surface, BA has the lowest binding energy, which is due to the lowest hardness parameter, and NNO has the highest binding energy, which is due to the highest dipole moment despite its small hardness parameter.

METHODS

For DFT calculation, NWChem was employed, which uses the Gaussian basis set. The B3LYP functional was used for exchange-correlation interaction between electrons, and the 6-311G+ (d,p) basis sets were used for all the atoms. Solvation effect was considered by using COSMO (COnductor-like Screening MOdel), in which the dielectric constant of solvent was set to 78.54 of water. For dispersion correction, DFT-D method of Tkatchenko and Scheffler (TS) was used. MD simulations were performed by using GULP (General Utility Lattice Program) code with Dreiding forcefield and atomic Hirshfeld charges from DFT calculations. MD simulations were performed on the conditions of NVT ensemble with a step of 1 fs and simulation time of 500 ps at 298 K and 323 K. To consider solvation effect, 1,000 water molecules were inserted into the box.

Kinetic simulation study of femtosecond laser processing of graphene oxide: first-principles

CONTEXT

Organic-inorganic nanoparticles have received extensive attention in various fields due to their unique physicochemical properties and biological activities. Among these nanoparticles, graphene oxide (GO) has emerged as a promising material, and thus, its application in biomedical fields is of great interest. Coating graphene oxide on the surface of implants can enhance its properties such as antibacterial and cell proliferation promotion, but the osteogenic properties of graphene oxide coating need further improvement, and the chance of acute inflammation triggered by local reactive oxygen species accumulation needs to be reduced. High-precision modulation of graphene oxide surface micro/nanomorphology and chemical composition can be achieved using femtosecond laser processing technology to improve its performance while also reducing the oxygen content of the graphene oxide surface to some extent. In this paper, the properties of graphene oxide were investigated by kinetic simulations based on the first-principle. The results show that the band gap of graphene oxide changes from 0.386 to 0.021 eV; the work function changes from 4.882 to 4.64 eV; the size and number of peaks in the radial distribution function decreases; and the intensity of the scatter X-ray peak becomes smaller under the action of femtosecond laser, indicating that the oxygen-containing functional groups on the surface of graphene oxide are disrupted, which provides a basis for its potential application in the medical field.

METHODS

To investigate the properties of graphene oxide, SEM, XPS, Raman, and FTIR characterizations were first used to determine the oxygen-containing functional group species on the surface of graphene oxide. The structural model of graphene oxide was then modeled for density flooding theory (DFT) simulations using Biovia Materials Studio software, which was implemented in the CASTEP code. Our DFT calculations were performed using the generalized gradient approximation (GGA) as parameterized by the Perdew-Burke Ernzerhof (PBE) exchange-correlation functional. Additionally, we employed the norm-conserving pseudopotential to treat core electrons.

Photoelectric structure and magnetic changes caused by niobium disulfide adsorbing (non)-metal atoms under defects

CONTEXT

The property transition between metal and semiconductor is the key to improving the properties of transition metal dichalcogenides (TMDCs). The adsorption of the NbS₂ compound in the defect state was adjusted for the first time. The hybrid system overwrites the original surface mechanism of NbS₂ and induces indirect band gaps. This modulation mode makes NbS₂ convert into a semiconductor and effectively improves the catalytic activity of the material in the system. In addition, the original local magnetic moment of the compound is concentrated in the vacancy region and is improved. The optical properties of the adsorption system indicate that NbS₂ compounds can be effectively applied in visible and low-frequency ultraviolet regions. This provides a new idea for the design of the NbS₂ compound as a two-dimensional photoelectric material.

METHODS

In the study, we assume that only one atom is adsorbed on the NbS₂ supercell of the defect, and the distance between the two adjacent atoms exceeds 12.74 Å, so the interaction between atoms is ignored in the study. Adsorbed atoms include nonmetallic elements (H, B, C, N, O, F), metallic elements (Fe, Co), and noble metal elements (Pt, Au, Ag). The density functional theory (DFT) was used in the experiment. The non-conservative pseudopotential method was used in the calculation to optimize the crystal structure geometrically. The approximate functional is Heyd-Scuseria-Ernzerhof (HSE06). The calculation method includes the spin-orbit coupling (SOC) effect. The crystal relaxation optimization uses a 7 × 7 × 1 k point grid to calculate niobium disulfide's photoelectric and magnetic properties. A vacuum space of 15Å is introduced in the direction outside the plane, and the free boundary condition is adopted to avoid the interaction between atomic layers. For the convergence parameter setting, the interatomic force of all composite systems is less than 0.03 eV/Å, and the lattice stress is less than 0.05 Gpa.

Highly exfoliated graphitic carbon nitride for efficient removal of wastewater pollutants: Insights from DFT and statistical modelling

The present work entails the synthesis of thermally modified graphitic carbon nitride (GCN) using a two-step thermal treatment procedure and its subsequent use in the photocatalytic reduction of toxic pollutants such as rhodamine B dye (RhB) and chromium (VI) (Cr(VI)) from aquatic environments. The as-synthesised exfoliated GCN (GCNX) is characterised by X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), Brunauer-Emmett-Teller analysis (BET), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). These characterisations helped to elucidate the phase formation, chemical structure, composition, surface area, optical properties, and morphology of the sample. With assistance from a visible light source, GCNX can degrade RhB dye within 30 min in the presence of hydrogen peroxide (H₂O₂) and reduce Cr(VI) to Cr(III) in under 2 h in the presence of formic acid (FA/HCOOH). Variations in different catalytic parameters, including catalyst amount, pH of the solution, initial RhB or Cr(VI) concentration, and variation in H₂O₂ or FA concentration, are performed to inspect their effects on the photodegradation activity of GCNX. Moreover, the GCNX catalyst exhibits impressive stability and reusability. A thorough statistical evaluation follows the response surface methodology to understand the complex interaction between the factors contributing to the catalytic activity. The band alignment of differently functionalised GCN blocks in their pristine form and their H₂O₂/FA-adsorbed states is investigated using first-principles calculations to provide a further understanding of the RhB and Cr(VI) reduction mechanisms. The modified GCN can thus be effectively employed as a low-cost material for removing contamination from aquatic environments.

Copper content effects on passive film of modified 00Cr20Ni18Mo6CuN super austenitic stainless steels in acidic environment

To provide a theoretical basis for the design of super austenitic stainless steel used in flue gas desulfurization environment, by changing the Cu content in 00Cr20Ni18Mo6CuN super austenitic stainless steel to explore the influence of Cu on its corrosion resistance, by electrochemical methods, XPS and first-principle computational simulations. The results show that Cu promotes the selective dissolution of Fe, Cr and Mo in stainless steel, and the copper content changes the proportion of compounds in the passive film, as well as its surface quality, resistance and defect density. The addition of one Cu atom increases the adsorption energy and work function of NH₃ on Cr₂O₃ surface, reduces the charge transfer and hybridization. However, when the Cu content exceeds 1 wt%, the surface of the passive film is loose and has many defects. The appearance of oxygen vacancy and two Cu atoms leads to the decrease of adsorption energy and work function, and enhances the charge transfer and hybrid effect. The optimal Cu content is obtained through research, which not only improves the corrosion resistance of 00Cr20Ni18Mo6CuN super austenitic stainless steel in flue gas desulfurization environment, prolonging the service life of 00Cr20Ni18Mo6CuN super austenitic stainless steel, but also has practical application value.

Effect of hydrogen coverage on elastic and optical properties of silicene: a first-principle study

The structural, electronic, and optical properties of hydrogenated silicene have been investigated using first-principles DFT calculations. Compared to pristine silicene, hydrogenated silicene exhibits high stability, reduced anisotropy, and less birefringence. Hydrogenated silicene shows a constant refractive index in the visible region, increasing exponentially in silicene. The elastic and optical parameters such as Young's modulus (Y), Poisson's ratio (ν), bulk modulus (B), shear modulus (G), dielectric constant ε(0), refractive index n(0), conductivity threshold (E_th), birefringence Δn(0), and plasmon energy (ħω_p) were calculated for the first time for different hydrogen coverage on silicene, which is crucial in the applications of linear and non-linear optoelectronic devices. The estimated parameters agree well with the available experimental and reported values.

Electronic structure and optical properties of B-, N-, and BN-doped black phosphorene using the first-principles

The structural stability, electronic structure, and optical properties of BN-doped black phosphorene systems at different concentrations were investigated using a density generalized theory approach based on the first principles. BN-doped black phosphorene was found to be more stable than B and N atom doping. With the increase of doping concentration, the stability of the structure gradually decreases, and the structure of the system with 25% doping concentration is the most stable. The intrinsic and N-doped black phosphorenes are direct bandgap semiconductors, and B and BN doping make the black phosphorene change from direct bandgap to the indirect bandgap. The total density of states is mainly contributed by the p-state electrons of the B and P atoms, and the N atoms have a role in the local density of states with little contribution to the overall one. The black phosphorene undergoes charge transfer between the B and N atoms. The amount of charge transfer increases with the increase of doping concentration. The BN-doped black phosphorene system is blue-shifted at the absorption and reflection peaks compared to the intrinsic black phosphorene system. From the dielectric constant, it is found that the doped system is shifted towards higher energy at the highest peak, leading to an increase in the intensity of the electric field generated by light, which is beneficial to increase the efficiency of photovoltaic power generation. The photoconductivity decreases and shifts toward higher energy after doping, with the most pronounced performance at BN doping concentrations of 12.5% and 25%.

Asymmetric surfaces endow Janus bismuth oxyhalides with enhanced electronic and catalytic properties for the hydrogen evolution reaction

The electronic and catalytic properties of Janus bismuth oxyhalide (Bi₂O₂XY, where X/Y = Cl, Br, or I, and X ≠ Y) for the hydrogen evolution reaction (HER) are evaluated through first-principles calculations. Janus Bi₂O₂XY shows an enhanced separation efficiency of electron-hole pairs and an augmented utilization of solar energy due to Janus asymmetry. The asymmetric halogen surfaces on both sides of Janus Bi₂O₂XY induce an electrostatic potential difference, which leads to a staggered band alignment. The solar-to-hydrogen (STH) efficiencies of Janus Bi₂O₂BrI and Bi₂O₂ClI have greatly improved compared to those of pristine BiOBr and BiOCl. Additionally, Janus Bi₂O₂XY achieves stronger internal electric fields (IEFs) and a more suitable Gibbs free energy of hydrogen adsorption (ΔG_H) than pristine BiOX. Moreover, the halogen layer with a smaller electronegativity in Janus Bi₂O₂XY forms a stronger IEF with the oxygen layer; consequently, the ΔG_H of terminations value is closer to the ideal value for the HER. The localized edge states in the p-orbital density of states (DOS) projected onto O atoms are responsible for the HER activity of terminations. This work provides a comprehensive understanding of Janus Bi₂O₂XY for the HER and provides a strategy for improving photocatalysis.

Structural stability, elasticity, thermodynamics, and electronic structures of L12-type Ni3X (X = Al, Ti, V, Nb) phases under external pressure condition

In this paper, the effect of pressure on the structural stability, elasticity, thermodynamics, and associated electronic structure of L1₂-type Ni₃X (X = Al, Ti, V, Nb) phases is investigated using a first-principles approach. It is shown that pressure leads to volume compression of the Ni₃X phase and reduction of the lattice parameters. The increase of pressure promotes the increase of elastic constants, bulk modulus, shear modulus, and Young's modulus. And there is an extremely strong linear correlation between the pressure and the elastic constants. The calculated elastic constants indicate that the pressure leads to strong mechanical stability and ductility of the Ni₃X phase. Mechanical anisotropy of the Ni₃X phase also increases with increasing pressure. The electronic analysis shows that the increase in pressure leads to enhanced Ni-d-orbitals and X-d-orbitals hybridization and increased electron transfer. The order in terms of electron accumulation intensity is Ni₃Ti > Ni₃Nb > Ni₃V > Ni₃Al. It is more directly reflected in the charge density difference diagram. This is in agreement with the results of the enthalpy of formation (ΔH) and Debye temperature (Θ_D) analysis.

Understanding the roles of copper dopant and oxygen vacancy in promoting nitrogen oxides removal over iron-based catalyst surface: A collaborative experimental and first-principles study

In this work, we proposed a novel strategy of copper (Cu) doping to enhance the nitrogen oxides (NO_x) removal efficiency of iron (Fe)-based catalysts at low temperature through a simple citric acid mixing method, which is critical for its practical application. The doping of Cu significantly improves the deNO_x performance of Fe-based catalysts below 200 °C, and the optimal catalyst is (Cu_0.22Fe_1.78)_1-δO₃, which deNO_x efficiency can reach 100% at 160-240 °C. From the macro aspects, the main reasons for the excellent catalytic activity of the (Cu_0.22Fe_1.78)_1-δO₃ catalyst are the large number of oxygen vacancies (O_vac), appropriate Fe³⁺ and Cu²⁺ contents, stronger surface acidity and redox ability. From the micro aspects, the O_vac plays a key role in enhancing molecular adsorption, oxidation, and the deNO_x reaction over the Fe-based catalyst surface, which promoting order is CuO_vac > O_vac > Cu. This work provides a new insight for the mechanism study of oxygen vacancy engineering and also accelerates the development of CuFe bimetal composite catalysts at low temperature.

Adsorption characteristics of citric acid on Fe3O4 (001), (011), and (111) surfaces

Magnetite (001), (011), and (111) surfaces were the focus of our study. Magnetite (001) surface has two different terminations, that is, Fe_tet and 2Fe_oct4O. Magnetite (011) surface has two different terminations, that is, 2Fe_oct4O and 2Fe_tet2Fe_oct4O. Magnetite (111) surface has six different terminations, that is, Fe_tet1, Fe_oct, Fe_tet2, 3Fe_oct, 4O₁, and 4O₂. Comparing surface energies of (001), (011), and (111) surfaces, (001) has the smallest surface energy, and (111) has the largest surface energy except for Fe_oct termination, which means that (001) surface is the easiest to be cleaved, followed by (011) and (111) surfaces. Comparing adsorption energies of citric acid onto (001), (011), and (111) surfaces, (111) has the largest adsorption energies except for Fe_tet2 termination, and (001) has the smallest adsorption energies, which means that (111) surface is the most active for citric acid adsorption, followed by (011) and (001) surfaces. PDOS (partial density of states) of citric acid adsorbed onto (001), (011), and (111) surfaces with different terminations shows that 3d orbital of Fe of magnetite surface does not contribute to the adsorption, and 4s orbital of Fe of magnetite surface and 2s and 2p orbitals of O of citric acid contribute to the adsorption.

The stability, structural, electronic, and optical properties of hydrogenated silicene under hydrostatic pressures: a first-principle study

The structural, electronic, and optical properties of hydrogenated silicene have been studied under different hydrostatic pressures using first-principle calculations. The binding energy and band structure have been calculated for chair (C-) and boat (B-) structures, which are having good stability at 0 GPa, 3 GPa, 6 GPa, 9 GPa, 12 GPa, 15 GPa, and 18 GPa hydrostatic pressures. Stability has been verified using binding energy and phonon calculations. The C- and B-structures have become metallic and unstable at 21 GPa. The optical properties of B-configuration have been studied in the energy range of 0-20 eV. Five optical parameters such as conductivity threshold (σ_th), dielectric constant ε(0), refractive index n(0), birefringence Δn(0), and plasmon energy (ħω_p) have been calculated for the first time under different hydrostatic pressures. The calculated values are in good agreement with the reported values at 0 GPa.

Ab initio study of photocatalytic characteristics of graphitic carbon nitride assisted by oxalic acid

Using density functional theory, structural, electronic, and optical properties of GCN (graphitic carbon nitride) and OAGCN (graphitic carbon nitride combined with oxalic acid) were studied. By comparing HOMOs and LUMOs and excitonic binding energies, OAGCN has lower photoinduced electron-hole recombination rate than GCN. VBM and CBM levels of GCN and OAGCN were calculated, which shows that for GCN, only the electron at CBM contributes to produce radicals for removing pollutants, and for OAGCN, both the electron at CBM and the hole at VBM contribute to produce radicals for removing pollutants. In total, it can be said that OAGCN has higher photocatalytic activity than GCN.

Influence of halogen atom substitution and neutral HCN/anion CN- Lewis base on the triel-bonding interactions

Triel-bonding interactions composed of Lewis acid TrOHH₂/TrOH₂X/TrOHX₂ (Tr = B, Al, Ga; X = F, Cl, Br) molecule and Lewis base neutral HCN or anionic CN^- molecule are of research significance in bond properties, which has been investigated at MP2/aug-cc-pVTZ theory level. It is also feasible to study the halogen atom substituent effect and influence of different Lewis bases on the formation of triel bond. AIM analyses reveal that Tr (Tr = B, Al, Ga)···N bond critical point (BCP) exists in all studied triel bond. In the formation of triel bonding, compared with Lewis base HCN molecule, Lewis base anionic CN^- can participate in a stronger triel bond. Specifically, the structural change, deformation energy, and charge transfer of CN^- complexes are all larger than that of HCN complexes. In addition, halogen atom substitution effect is also discussed. MEP value and binding energy of HCN and CN^- complexes all increase after replacing one or two hydrogen atoms by halogen atoms (F, Cl, Br) in Lewis acid. Especially, replacing two hydrogen atoms by halogen atoms in Lewis acid has more remarkable enhancement in MEP value and binding energy than that of replacing only one hydrogen atom. After replacement, binding energy can be increased by 21.77 kcal/mol. The neutral and anionic triel-bonded complexes composed by Lewis acid TrOHH₂/TrOH₂X/TrOHX₂ (Tr = B, Al, Ga; X = F, Cl, Br) with Lewis base HCN and CN^- are systematically investigated at MP2/aug-cc-pVTZ level. The neutral (HCN) triel bonding is weaker than the anionic (CN^-) triel bonding due to the smaller MEP value of the neutral HCN molecule. The replacement of hydrogens (-H) in Lewis acid by electron-withdrawing groups (-F, -Cl, -Br) has a prominent enhancement effect on the MEP value of π-hole and triel-bonding strength.

Adsorption of gas molecules of CH4, CO and H2O on the vanadium dioxide monolayer: Computational method and model

Inspired by the recent use of two-dimensional nanomaterials as gas sensors, we used density functional theory calculations to study the adsorption of gas molecules (CH$_4$, CO and H$_2$O) on sandwich vanadium dioxide tablets. The results showed that of all these gases, only the CH$_4$ gas molecule was the electron acceptor with significant charge transfer on the VO$_2$ sheet. The adsorption energies of CH$_4$, CO and H$_2$O are -229.5 meV, -239.1 meV and -388.3 meV, respectively. We have also compared the adsorption energy of three different gas molecules on the VO$_2$ surface, our calculation results show that when the three kinds of gases are adsorbed on the VO$_2$ surface, the order of the surface adsorption energy is H$_2$O$>$ CO$>$ CH$_4$. It is also found that after adsorption of CH$_4$, CO and H$_2$O molecules, the electronic properties of VO$_2$ sheet changed obviously. However, due to the strong adsorption of H$_2$O molecule on VO$_2$ sheet, it is difficult to desorption, which hinders its application in gas molecular sensors. The optical properties of VO$_2$ sheet are further calculated. The absorption of CH$_4$, CO and H$_2$O molecules is introduced to red-shift the dielectric function of the thin film, which indicates that the optical properties of the thin film have changed significantly. According to the change of optical properties of VO$_2$ sheet before and after molecular adsorption, VO$_2$ can be used as a highly selective optical gas sensor for CH$_4$, CO and H$_2$O detection. These results provide a new approach for the potential application of VO$_2$ based optical gas sensors.

Impact of gas adsorption on the stability and electronic properties of negative electron affinity GaAs nanowire photocathodes

The influence of CO, CO₂, H₂O, H₂ and CH₄ adsorption on the stability and electronic properties of negative electron affinity (NEA) GaAs nanowire surfaces activated by Cs/O and Cs/NF₃ are systematically investigated via first-principles. The calculations indicated that GaAs nanowires activated with 3Cs/O are more susceptible to the surface contamination. After residual gas molecule adsorption, 3Cs/O activated surfaces exhibit direct bandgap character, while 3Cs/NF₃ activated surfaces are inversely indirect bandgap. In addition, residual gas adsorption results in a notable increase of band gap, work function and electron affinity of GaAs nanowire surfaces. The incoporation of residual gas molecules also induces a new electric dipole [Cs-gas] with a direction from Cs to gas molecule. From the perspective of theoretical calculation, it is predicted that GaAs nanowires activated through Cs/NF₃ has a stronger stability compared with Cs/O in the aspect of gas exposure.

Ferroelectrically tunable magnetism in BiFeO3/BaTiO3 heterostructure revealed by the first-principles calculations

The perovskite oxide interface has attracted extensive attention as a platform for achieving strong coupling between ferroelectricity and magnetism. In this work, robust control of magnetoelectric (ME) coupling in the BiFeO3/BaTiO3 (BFO/BTO) heterostructure (HS) was revealed by using the first-principles calculation. Switching of the ferroelectric polarization of BTO induce large ME effect with significant changes on the magnetic ordering and easy magnetization axis, making up for the weak ME coupling effect of single-phase multiferroic BFO. In addition, the Dzyaloshinskii-Moriya interaction (DMI) and the exchange coupling constants J for the BFO part of the HSs are simultaneously manipulated by the ferroelectric polarization, especially the DMI at the interface is significantly enhanced, which is three or four times larger than that of the individual BFO bulk. This work paves the way for designing new nanomagnetic devices based on the substantial interfacial ME effect.

Spin Seebeck effect in bipolar magnetic semiconductor: A case of magnetic MoS2 nanotube

Bipolar magnetic semiconductors (BMSs) are a new member of spintornic materials. In BMSs, one can obtain 100% spin-polarized currents by means of the gate voltage. However, most of previous studies focused on their applications in spintronics instead of spin caloritronics. Herein, we show that BMS is an intrinsic model for spin Seebeck effect (SSE). Without any gate voltage and electric field, currents with opposite spin orientation are generated and flow in opposite directions with almost equal magnitude when simply applying a temperature bias. This is also due to the special electronic structure of BMS where the conduction and valence bands near the Fermi level belong to opposite spin orientation. Based on density function theory and non-equilibrium Green's function methods, we confirm the thermal-induced SSE in BMS using a case of magnetic MoS₂ nanotube. The magnitude of spin current in zigzag tube is almost four times higher than that in armchair tube. BMS is promising candidates for spin caloritronic applications.

A WS2 Case Theoretical Study: Hydrogen Storage Performance Improved by Phase Altering

Hydrogen is a clean energy with high efficiency, while the storage and transport problems still prevent its extensive use. Because of the large specific surface area and unique electronic structure, two-dimensional materials have great potential in hydrogen storage. Particularly, monolayer 2H-WS₂ has been proven to be suitable for hydrogen storage. But there are few studies concerning the other two phases of WS₂ (1T, 1T') in hydrogen storage. Here, we carried out first-principle calculations to investigate the hydrogen adsorption behaviors of all the three phases of WS₂. Multiple hydrogen adsorption studies also evaluate the hydrogen storage abilities of these materials. Comprehensive analysis results show that the 1T'-WS₂ has better hydrogen storage performance than the 2H-WS₂, which means phase engineering could be an effective way to improve hydrogen storage performance. This paper provides a reference for the further study of hydrogen storage in two-dimensional materials.

Rich topological nodal line bulk states together with drum-head-like surface states in NaAlGe with anti-PbFCl type structure

The band topology in condensed matter has attracted widespread attention in recent years. Due to the band inversion, topological nodal line semimetals (TNLSs) have band crossing points (BCPs) around the Fermi level, forming a nodal line. In this work, by means of first-principles, we observe that the synthesized NaAlGe intermetallic compound with anti-PbFCl type structure is a TNLS with four NLs in the k_z = 0 and k_z = π planes. All these NLs in NaAlGe exist around the Fermi level, and what is more, these NLs do not overlap with other bands. The exotic drum-head-like surface states can be clearly observed, and therefore, the surface characteristics of NaAlGe may more easily be detected by experiments. Biaxial strain has been explored for this system, and our results show that rich TNL states can be induced. Furthermore, the spin-orbit coupling effect has little effect on the band structure of NaAlGe. It is hoped that this unique band structure can soon be examined by experimental work and that its novel topological elements can be fully explored for electronic devices.

Novel topological nodal lines and exotic drum-head-like surface states in synthesized CsCl-type binary alloy TiOs

Very recently, searching for new topological nodal line semimetals (TNLSs) and drum-head-like (DHL) surface states has become a hot topic in the field of physical chemistry of materials. Via first principles, in this study, a synthesized CsCl type binary alloy, TiOs, was predicted to be a TNLS with three topological nodal lines (TNLs) centered at the X point in the kx/y/z = π plane, and these TNLs, which are protected by mirror, time reversal (T) and spatial inversion (P) symmetries, are perpendicular to one another. The exotic drum-head-like (DHL) surface states can be clearly observed inside and outside the crossing points (CPs) in the bulk system. The CPs, TNLs, and DHL surface states of TiOs are very robust under the influences of uniform strain, electron doping, and hole doping. Spin-orbit coupling (SOC)-induced gaps can be found in this TiOs system when the SOC is taken into consideration. When the SOC is involved, surface Dirac cones can be found in this system, indicating that the topological properties are still maintained. Similar to TiOs, ZrOs and HfOs alloys are TNLSs under the Perdew-Burke-Ernzerhof method. The CPs and the TNLs in both alloys disappear, however, under the Heyd-Scuseria-Ernzerhof method. It is hoped that the DHL surface property in TiOs can be detected by surface sensitive probes in the near future.

Solvent effect on the photophysical properties of thermally activated delayed fluorescence molecules

As the third-generation organic electroluminescent materials, thermally activated delayed fluorescence (TADF) molecules have become the research focus recently. Significant solvent effect on TADF molecules were found experimentally, while theoretical investigations are quite limited. In this work, the solvent effect on photophysical properties of DCBPy and DTCBPy are investigated with first-principles calculations. The solvent polarity has slight influence on the molecular geometries and orbitals, while it can decrease the energy gap between the first singlet excited state (S1) and first triplet excited state (T1) significantly. Both the oscillator strength and the radiation rates of S1 increase with larger solvent polarity. The large energy gap between S1 and T1 induce negligible intersystem crossing (ISC) and reverse ISC rates between them, which also indicates higher triplet excited states are involved in the up-conversion process. Our results provide valuable information about solvent influence on the light-emitting properties of TADF molecules, which could help one better understand the light-emitting mechanism of them and favor the design of TADF molecules.

Tribological investigation of additive manufacturing medical Ti6Al4V alloys against Al2O3 ceramic balls in artificial saliva

Additive manufacturing Ti6Al4V alloys have found their potential applications in artificial teeth and hip joints. In this work, the relationships between wear resistance, hardness and microstructure of Ti6Al4V alloys fabricated using various routes were investigated in artificial saliva. The results indicate that comparing with wrought and wrought + heat treated (HT) samples, the as-SLMed samples with hcp-α' martensite and few bcc-β phase exhibit higher hardness (∼410 HV) and better wear resistance. The as-SLMed samples, however, exhibit the worst wear resistance when wear direction is parallel to the molten pool line on XOZ-plane due to containing the softer fusion zone. Finally, the wear mechanism is discussed in detail, mainly including the abrasive and adhesive wear mechanism. The high hardness of matrix as well as the strong adhesion between the hardened layer, oxide layer and matrix are indispensable conditions for maintaining the optimum wear resistance.

Mechanism of Yttrium composite inclusions on the localized corrosion of pipeline steels in NaCl solution

In order to solve the problem of where, why, and how to start pitting, it is necessary to study the influence of different dissolution activity of the internal heterogeneous structures of the complex inclusions. In this paper, mechanism of internal activity difference of two typical Yttrium composite inclusions on pitting corrosion is revealed from atomic scale by using immersion test, FE-SEM/EDS analysis and first-principles calculations. The results show that, for Mg-Y-S composite inclusions, pitting potential is lower than that of the matrix, therefore, The matrix around the composite inclusions dissolves preferentially; for Y-S-O composite inclusions with core-shell structure, Y-O inclusions in the shell are deformed and cracked due to the internal stress of the matrix and Y-S during the immersion process, resulting in the simultaneous dissolution of inclusions and steel matrix.

Insight into the robust multiple Dirac-cones in perovskite R3¯c phase CuBO3 semimetal from first-principles

Motivated by a related recent study (Jiao et al. PRL 119, 016403 (2017)), in this work, a new R3¯c type semimetal has been calculated based on the first-principles method. We observed that CuBO₃ showed robust multiple Dirac-cones (DCs) near the Fermi level. Also, we found that these DCs were coming from the hybridization between O-p and Cu-d orbits. As a medium state between normal insulating state and topological insulating state, Dirac semimetal is a new class of materials due to its novel physical properties. Moreover, for CuBO₃, the Dirac-like band crossings are dispersed in a linear pattern across a very large energy range. In order to guide the experiment, the thermal stability of CuBO₃ has been studied through ab initio molecular dynamic simulations. Finally, we are keen to emphasize that the specific space of this group allows for the three-dimensional Dirac point to be used as a symmetric protection for degeneracy. There may be many other three-dimensional Dirac semimetals in the R3¯c phase of crystallization that have not yet been discovered. Thus, more attention to these materials is required in the future.

Composition Dependence of Structural and Electronic Properties of Quaternary InGaNBi

To realize feasible band structure engineering and hence enhanced luminescence efficiency, InGaNBi is an attractive alloy which may be exploited in photonic devices of visible light and mid-infrared. In present study, the structural, electronic properties such as bandgap, spin-orbit splitting energy, and substrate strain of InGaNBi versus In and Bi compositions are studied by using first-principles calculations. The lattice parameters increase almost linearly with increasing In and Bi compositions. By bismuth doping, the quaternary InGaNBi bandgap could cover a wide energy range from 3.273 to 0.651 eV for Bi up to 9.375% and In up to 50%, corresponding to the wavelength range from 0.38-1.9 µm. The calculated spin-orbit splitting energy are about 0.220 eV for 3.125%, 0.360 eV for 6.25%, and 0.600 eV for 9.375% Bi, respectively. We have also shown the strain of InGaNBi on GaN; it indicates that through adjusting In and Bi compositions, InGaNBi can be designed on GaN with an acceptable strain.

Strain Tunable Bandgap and High Carrier Mobility in SiAs and SiAs2 Monolayers from First-Principles Studies

Searching for new stable free-standing atomically thin two-dimensional (2D) materials is of great interest in the fundamental and practical aspects of contemporary material sciences. Recently, the synthesis of layered SiAs single crystals has been realized, which indicates that their few layer structure can be mechanically exfoliated. Performing a first-principles density functional theory calculations, we proposed two dynamically and thermodynamically stable semiconducting SiAs and SiAs₂ monolayers. Band structure calculation reveals that both of them exhibit indirect band gaps and an indirect to direct band even to metal transition are found by application of strain. Moreover, we find that SiAs and SiAs₂ monolayers possess much higher carrier mobility than MoS₂ and display anisotropic transportation like the black phosphorene, rendering them potential application in optoelectronics. Our works pave a new route at nanoscale for novel functionalities of optical devices.

Design rules of heteroatom-doped graphene to achieve high performance lithium-sulfur batteries: Both strong anchoring and catalysing based on first principles calculation

A number of observations have been reported on chemical capture and catalysis of anchoring materials for lithium-sulfur batteries. Here, we propose the design principles for the chemical functioned graphene as an anchor material to realize both strong chemical trapping and catalysis. Through the first principle, the periodic law is calculated from the theory. Seven different co-doping series were investigated, e.g. MN₄@graphene (M = V, Cr, Mn, Fe, Co, Ni, and Cu). From binding energy, partial density of state, and charge density difference analysis, the FeN₄ and CrN₄ co-doped graphene show good performance for the lithium-sulfur battery from both strong anchoring and catalytic effects. For the most kinds of Li₂S_x (x = 1, 2, 4, 6, 8) absorption, two combinations can be achieved, including S-bonding and Li-bonding. The competition between the MS and the NLi shows the main difference of the co-doped configurations. Moreover, the S-bonding systems have better performance for both moderate chemical trapping and strong catalysis. The binding energies of Li₂S_x and Li decomposed properties considered as the key descriptors for the rational design of lithium-sulfur battery. Lastly, we offer design rules for high performance lithium-sulfur batteries based on the chemical functional graphene materials.

Interplay between habitat subdivision and minimum resource requirement in two-species competition

This paper explores the effects of increasing spatial subdivision of habitat on competition between two species. An increase in the degree of subdivision without any increase in the total amount of resources in the environment leads to smaller patch sizes, and thus, fewer individuals supported per patch. This fact suggests that when the degree of subdivision is high, the minimum resources that an individual must obtain before reproduction become important. Competition equations derived from first-principles that incorporate the minimum resource requirement are employed to investigate the effects of spatial subdivision and how these effects depend on the minimum requirements of the two species, type of resource competition such as scramble or contest, and spatial aggregation level of individuals. The results show that increased subdivision leads to changes in "effective fecundities" of the species, and consequently, affects their competitive superiority. Species coexistence is promoted at intermediate subdivision levels, especially if there is a trade-off between the minimum resource requirement and inherent fecundity. The range of subdivision in which coexistence occurs depends on the spatial aggregation of individuals and inequality in competitive ability between the species.

Time-dependent density functional theory study on the excited-state hydrogen-bonding characteristics of polyaniline in aqueous environment

A theoretical study was carried out to study the excited-state of hydrogen-bonding characteristics of polyaniline (PANI) in aqueous environment. The hydrogen-bonded PANI-H₂O complexes were studied using first-principles calculations based on density functional theory (DFT). The electronic excitation energies and the corresponding oscillator strengths of the low-lying electronically excited states for hydrogen-bonded complexes were calculated by time-dependent density functional theory (TDDFT). The ground-state geometric structures were optimized, and it is observed that the intermolecular hydrogen bonds CN⋯HO and NH⋯OH were formed in PANI-H₂O complexes. The formed hydrogen bonds influenced the bond lengths, the charge distribution, as well as the spectral characters of the groups involved. It was concluded that all the hydrogen-bonded PANI-H₂O complexes were primarily excited to the S1 states with the largest oscillator strength. In addition, the orbital transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) involved intramolecular charge redistribution resulting to increase the electron density of the quinonoid rings.

Structural Properties and Phase Transition of Na Adsorption on Monolayer MoS2

First-principles calculations are performed to investigate the structural stability of Na adsorption on 1H and 1T phases of monolayer MoS2. Our results demonstrate that it is likely to make the stability of distorted 1T phase of MoS2 over the 1H phase through adsorption of Na atoms. The type of distortion depends on the concentration of adsorbed Na atoms and changes from zigzag-like to diamond-like with the increasing of adsorbed Na atom concentrations. Our calculations show that the phase transition from 1H-MoS2 to 1T-MoS2 can be obtained by Na adsorption. We also calculate the electrochemical properties of Na adsorption on MoS2 monolayer. These results indicate that MoS2 is one of potential negative electrodes for Na-ion batteries.

Structural and electronic properties of two-dimensional stanene and graphene heterostructure

Structural and electronic properties of two-dimensional stanene and graphene heterostructure (Sn/G) are studied by using first-principles calculations. Various supercell models are constructed in order to reduce the strain induced by the lattice mismatch. The results show that stanene interacts overall weakly with graphene via van der Waals (vdW) interactions. Multiple phases of different crystalline orientation of stanene and graphene could coexist at room temperature. Moreover, interlayer interactions in stanene and graphene heterostructure can induce tunable band gaps at stanene's Dirac point, and weak p-type and n-type doping of stanene and graphene, respectively, generating a small amount of electron transfer from stanene to graphene. Interestingly, for model [Formula: see text] , there emerges a band gap about 34 meV overall the band structure, indicating it shows semiconductor feature.

Dramatically Enhanced Visible Light Response of Monolayer ZrS2 via Non-covalent Modification by Double-Ring Tubular B20 Cluster

The ability to strongly absorb light is central to solar energy conversion. We demonstrate here that the hybrid of monolayer ZrS₂ and double-ring tubular B₂₀ cluster exhibits dramatically enhanced light absorption in the entire visible spectrum. The unique near-gap electronic structure and large built-in potential at the interface will lead to the robust separation of photoexcited charge carriers in the hybrid. Interestingly, some Zr and S atoms, which are catalytically inert in isolated monolayer ZrS₂, turn into catalytic active sites. The dramatically enhanced absorption in the entire visible light makes the ZrS₂/B₂₀ hybrid having great applications in photocatalysis or photodetection.

The electronic and optical properties of quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs: a first-principles study

First-principles calculations based on density functional theory have been performed for the quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1-x-y N x Bi y alloy with y/x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1-x-y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1-x-y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1-x-y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1-x-y N x Bi y quaternary alloys in optoelectronic devices.